Method and apparatus for resistance heating slotted tubes

ABSTRACT

A method and apparatus for resistance heating an elongated tube having a slot-like area therein extending generally longitudinally over a portion of the length, which tube is to be subsequently formed at the slot area following heating. The tube is clamped between first and second pairs of contacts spaced immediately adjacent each end thereof. Third and fourth pairs of contacts are then clamped over the tube adjacent each end of the slot-like area and between the first and second pairs of contacts. An electrical current is then caused to flow through the tube between the first and third and the second and fourth pairs of contacts to effect heating of the tube ends. The third and fourth pairs of contacts are then removed from contact with the tube and an electrical current is caused to flow through the tube between the first and second pairs of contacts to effect desired heating over the entire length of tube.

United States Patent 1 Arnosky METHOD AND APPARATUS FOR RESISTANCEHEATING SLOTTED TUBES lnventorz- Joseph E. Arnosky, Broadview Heights,Ohio 44147 Park-Ohio Industries Inc., Cleveland,0hio

Filed: Sept. 7, 1971 Appl. No.1 177,932

Assignee:

US. Cl. ..2l9/l56, 219/56, 219/58, 219/59, 219/67 Int. Cl. ..C21d 9/62Field of Search ..219/156, 59, 64,

References Cited UNITED STATES PATENTS June 5, 1973 [57] ABSTRACT Amethod and apparatus for resistance heating an elongated tube having aslot-like area therein extending generally longitudinally over a portionof the length, which tube is to be subsequently formed at the slot areafollowing heating. The tube is clamped between first and second pairs ofcontacts spaced immediately adjacent each end thereof. Third and fourthpairs of contacts are then clamped over the tube adjacent each end ofthe slot-like area and between the first and second pairs of contacts.An electrical current is then caused to flow through the tube betweenthe first and third and the second and fourth pairsof contacts to effectheating of the tube ends. The third and fourth pairs of contacts arethen removed from contact with the tube and an electrical current iscaused to flow through the tube between the first and second pairs ofcontacts to effect desired heating over the entire length of tube.

11 Claims, 4 Drawing Figures PATENTEUJJH 5% 3,737. 618

INVENTOR. JQSEPH E. ARNOSKY 2% vfigy AT TOR NEYS.

METHOD AND APPARATUS FOR RESISTANCE HEATING SLOTTED TUBES Thisapplication pertains to the art of resistance heating and moreparticularly to a method and apparatus for resistance heating anelongated slotted workpiece.

The invention is particularly applicable to resistance heating slottedtubes which are to be formed at least at the slot area following heatingand will be described with particular reference thereto; however, itwill be appreciated that the invention has broader applications and maybe employed in any instance where elongated workpieces having at leastone aperture therein are de-:

sired to be uniformly heated over the entire length thereof.

Previous apparatus and methods for resistance heating elongated slottedworkpieces have generally comprised placing the tube between first andsecond pairs of spaced apart heating contacts so that the tube was heldtherebetween at substantially the end points thereof. An electricalcurrent was then caused to flow through the tube between these pairs ofheating contacts in order that the desired resistance heating would beeffected. However, in using this approach for elongated slotted tubes,certain inherent drawbacks were present making it virtually impossibleto obtain uniform heating over the entire tube length: This, of course,was primarily due to the presence of an elongated slot-like area in thetube itself. In resistance heating, there is an actual current flowthrough a workpiece being heated and, as current generally seeks thepath of least resistance, the tube is heated to substantially highertemperatures along the sides of the slotted areas than at the ends ofthese areas and the ends of the tube itself. This,

of course, is because there is less tube area to be heated along thesides of the slots so that the current flow is concentrated at that areato thereby cause a faster heating rate. The result has been ineffectiveand nonuniform heating which left cold spots along certain areas of thetubes. These cold spots oftentimes created difficulties when the formingstep was attempted such that undesirable scrap workpieces weregenerated. v

The present invention contemplates a new method and apparatus whichovercome the above referred problems and provides a new method andapparatus for heating elongated slotted tubes which is economical toemploy, provides uniform heating over substantially the entire tubelength and is readily adaptable to use with other elongated workpieceshaving slotted or other recess areas therein.

In accordance with. one aspect of the present invention, there isprovided a method of heating an elongated workpiece having first andsecond terminal end portions and an intermediate portion having anintermediate portion having an aperture therein comprising a. clampingthe workpiece between first and .second pairs of contacts at first andsecond spaced positions along the workpieces;

b. clamping the workpiece between third and fourth pairs of contacts atthird and fourth spaced positions between the first and second positionsrespectively with the third and fourth positions each being disposedadjacent an end of the slot-like area; and, y I

c. causing an electrical current to flow through the workpiece betweenthe first and third pairs of contacts and through the workpiece betweenthe second and fourth pairs of contacts.

In accordance with a more limited aspect of the present invention, themethod of resistance heating further includes the steps of removing thethird and fourth pairs of contacts from the clamping positions whenthose portions of the slotted tube disposed between the first and thirdpairs of contacts and the second and fourth pairs of contacts have beenheated to a predetermined desired temperature; and, causing anelectrical current to flow through the workpiece between the first andsecond pairs of contacts to heat the tube to a predetermined desiredtemperature over the entire length thereof.

In accordance with another aspect of the present invention, there isprovided an apparatus for heating an elongated workpiece having at leastone slot-like area extending longitudinally therealong. The apparatus includes first and second spaced apart pairs of contacts having a firstopened condition and a second workpiece clamping and heatingconditionatfirst and second positions adjacent the ends of the workpieceand first means for forcing the first and second pairsof contactsbetween the first and second conditions. Third and fourth pairs ofcontacts are spaced between the first and second pairs of contacts andfrom each other. These pairs of contacts have a third opened conditionand a fourth workpiece clamping and heating condition and furtherinclude means for forcing them between the third and fourth conditions.Means areincluded for supplying electrical current to the first andthird pairs of contacts when thefirst pair of contacts is in the secondcondition and the third pair of contacts is in the fourth condition andto the second and fourth pairs of contacts when the second pair ofcontacts is in the second condition and the fourth pair of contacts isin the fourth condition.

In accordance with a more limited aspect of the present invention, theapparatus includes means for supplying electrical current to the firstand second pairs of contacts when theyare in the second condition andthe third and fourth pairs of contacts are in the third condition.

The principal object of the present invention is the provision of amethod and apparatus for resistance heating an elongated slottedworkpiece which provides uniform heating over the entire workpiecelength.

Another object of the present invention is the provision of a method andapparatus for resistance heating an elongated slotted workpiece which issimple and economical to use. 5

Another object of the present invention is the provision of a method andapparatus for resistanceheating an elongated slotted workpiece whichmethod and apparatus are readily adaptable for use with elongatedworkpieces having any cross sectional configuration l FIG. 2 is a crosssectional view taken along lines 2--2' in FIG. 1 showing in particularthe type of heating contacts utilized.

FIG. 3 is a front view showing the first heating stage of the subjectnew method and apparatus for resistance heating; and,

FIG. 4 is a front view showing the second stage of the subject newmethod and apparatus for resistance heatmg.

Referring now to the drawings wherein the showings are for the purposesof illustrating the preferred embodiment of the invention only and notfor purposes of limiting same, the FIGURES show an elongated slottedtube A clamped in a heating positionbetween pairs of heating contacts ofresistance heating apparatus B.

More specifically, FIGS. 1 and 2 show the prior art apparatushereinbefore used where there is shown a length of steel tubing havingends 12, 14. In the preferred embodiment, tubing 10 is of a thin walltype (FIG. 2), although other types of tubing or elongated workpieceshave been heated by this type of apparatus. Disposed in tubing 10 andextending transversely therethrough is an elongated slot or aperturegenerally desig-' nated 18 and having parallel side wall portions 20,22and opposed radiused end portions 24,26 which interconnect the side wallportions. This type of slotted tube is used for a variety of purposes inthe industrial environment such as, for example, as the outer sleeve forproviding an adjustment device. Most often, a slotted area is machinesin tubing 10 and the tubing then heat treated. In FIG. 1, a pair ofcontact-arm assemblies generally designated 30,32 are shown in clampingengagement with the tube adjacent ends 12,14 respectively. Contact armassembly 30 includes a pair of opposed contact areas 34,36 and contactarm assembly 32 includes a pair of similarly opposed contact areas38,40. FIG. 2 shows contact arm assembly 30 in more detail, it beingunderstood that contact arm 32 is identical therewith except whereotherwise specifically noted..

Contact assemblies 34,36 include copper contact blocks 35,37respectively which include V-shaped workpiece receiving grooves 42,43therein which is known in the art. Contact assembly 34 is affixed to acontact arm 50 and contact assembly 36 is affixed to a contact arm 52,arms 50,52 being pivotally mounted relative to each other at pivot area54. The result of this arrangement is to provide a scissors-likestructure with the contact areas disposed at one end and a fluid powercylinder 56 disposed at the other and mounted to each of the contactarms by convenient means such as standard clevis mountings. Whencylinder 56 is moved to the extended position, contact areas 34,36 aremoved toward each other to engage a workpiece in grooves 42,43 ofcontact blocks 35,37. When cylinder 56 is retracted, the contact areasare moved arcuately away from each other to permit removal of one andplacement of another workpiece relative thereto. A current supplygenerator generally designated 60 is provided to selectively supplycurrent to contact blocks 35,37. The current supply source is alsoattached to the contact blocks of contact areas 38,40 to effect acurrent flow between assemblies 30,32 through tube 10.

In using the above described prior apparatus, contact arm assemblies30,32 are positioned away from each other in order that they will engagethe tube substantially adjacent ends 12,14 as it has been found and isknown that the most efficient resistance heating occurs throughout theworkpiece when so positioned. With the contact areas 34,36 and 38,40 ina first or spaced apart condition, the workpiece is positioned betweenthem and cylinders 56 energized to extend so that contact assemblies aremoved to a second or clamping and heating condition. Thereafterelectrical current is caused to flow through the workpiece to effect theheating. However, as current flow through any conductor has the tendencyto flow through the path of least resistance, the current flow linesthrough tube 10 in FIG. 1 are along lines a as shown therein. As can beseen, the areas of the tube extending coextensive with side walls 20,22of slot 18 receive the bulk of the cur rent flow and therefore heated toa far greater degree than that portion of tube 10 adjacent end wallportions 24,26 of the slot and ends 12,14 of the tube itself. a

To overcome these prior difficulties, the subject invention provides themethod and apparatus which will hereinafter be described with referenceto FIGS. 3 and 4. Like components will be described with like numeralsand new or additional components will be described with new numerals.With reference to FIG. 3, and in accordance with the present invention,a third contact arm assembly generally designated is disposed adjacentassembly 30 and a fourth contact arm assembly 72 is disposed adjacentassembly 32. Assembly 70 includes a pair of opposed contact areas 74,76and assembly 72 includes a pair of opposed contact areas 78,80. Thesecontact areas are similar to the previously hereinabove describedcontact areas. Further, contact arm assemblies 70,72 include power means(not shown) for moving the contact areas between a third spaced apartcondition and a fourth clamping condition in contact with the tube asalso has been hereinabove described.

In utilizing this structure, assemblies 30,32 are trans versely spacedapart from each other so that their respective contact areas will engagetube 10 immediately adjacent ends 12,14. Further, assemblies 70,72 arespaced inboard of assemblies 30,32 and transversely spaced apart fromeach other so that when their respective contact areas are moved to thefourth condition,

they will engage the tube immediately adjacent end wall portions 24,26.Means known in the art and generally designated 90,92 are provided toestablish electrical current flow through the tube between the contactareas of assemblies 30,70 and between the contact areas of assemblies32,72 respectively. When the tube is in position, clamped betweencontact areas of the contact arm assemblies 30,70 and 32,72 andelectrical supply means 90,92 are energized, the ends of the tube,outboard of and including end wall portions 24,26 are heated as shown bythe schematic current flow lines generally designated b. In thepreferred embodiment, when the temperature of those portions of the tubebeing heated have reached a temperature of approximately 2,000F.,electrical supply means 90,92 are deenergized and the contact areas ofassemblies 70,72 are moved to the third or spaced apart condition.-'This movement is best shown in FIG. 4.

Once the contact areas of assemblies 70,72 have been moved to the thirdcondition, an electrical current supply means generally designated 94interconnected between assemblies 30,32 is energized so as to providecurrent flow through tube between them as hereinabove previouslydescribed with reference to the Prior art. The lines of current flow areschematically shown in FIG. 4 by lines c. Because of the current flow,the principal portion of the tube heated is that section extending alongside wall portions 20,22 which was previously unheated and a portion ofthe tube between end 12 and end portions 24 and. end portions and end 14and end portion 26 which had previously .been heated to a temperature ofapproximately 2, O00F. As the end portions are also receiving someheating, they will not cool substantially while the initially unheatedportion is being heated to bring the tube to the final desiredtemperature. Once the desired temperature is obtained, the contact areasof contact arm assemblies 30,32 may be moved from the second heatingcondition shown in FIG. 4 to the first openedcondition and the tuberemoved therefrom, another unheated tube inserted and the processrepeated as desired. The heated tube may then be moved for furtherprocessing and forming as desired.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon the reading and understanding of this specification. It ismy intention to include all such modifications and alterations insofaras they come within the scope of the appended claims or the equivalentsthereof.

Having thus described my invention, I now claim: 1. A method ofresistance heating an elongated work piece having at least one slot-likearea extending generally-longitudinally along a portion of saidworkpiece, said method comprising the steps of:

clamping said workpiece between first and second pairs of contacts atfirst and second spaced positions along said workpiece;

-clamping said workpiece between third and fourth pairs of contacts atthird and fourth spaced positions between said first and secondpositions respectively with said third and fourth positions each beingdisposed adjacent an end of said slot-like area; and,

causing an electrical current to flow through said workpiece betweensaid first and third pairs of con- :tacts and through said workpiecebetween said second and fourth pairs of contacts.

2.The method as defined in claim 1 further including thesteps ofremoving said third and fourth pairs of contacts from. said clampingpositions when the portions of said-workpiece disposed between saidfirst and third pairs of contacts and said second and fourth pairs ofcontacts have been heated to a predetermined desired temperature; and,

causing an electrical current to flow through said .workpiece betweensaid first and second pairs of contacts to heat said elongated workpieceto a pre- I .determined desired temperature.

3. Themethod as defined in claim 1 wherein said step of clamping saidworkpiece at first and second spaced positions comprises the step ofclamping said workpiece adjacent the ends thereof.

4. A method of heating an elongated workpiece hav-- ing first and secondterminal end portions "and an intermediate portion having an aperturetherein, said workpiece in electrical contact with one of said terminalend portions; placing a second contacta'gains't said workpiece inelectrical contact with the other of'said terminal end portions; placinga third contact against said workpiece in electrical contact with saidintermediate portion at the end of said aperture adjacent said one ofsaid terminal end portions; placing a fourth contact against saidworkpiece in electrical contact with said intermediate portion at theend of said aperture adjacent said other of said terminal end portions;causing an electrical current to flow through said workpiece betweensaid first and said third contacts; and, causing an electrical currentto flow through said workpiece between said second and said fourthcontacts.

6. The method as defined in claim 5 wherein the step of resistanceheating substantially the entire workpiece comprises the steps orremoving said third and said fourth contacts from electrical contactagainst said intermediate portion and causing an electrical current toflow through said workpiece between said first and said second contacts.

7. An apparatus for resistance heating an elongated workpiece having atleast one slot-like area extending longitudinally therealong, saidapparatus comprising:

first and second spaced apart pairs of contacts, each pair having afirst opened condition and a second workpiece clamping and heatingcondition wherein when said firstand second pairs of contacts arein saidsecond condition, said first pair of contacts engages said wOrkpieceadjacent one end thereof and said second pair of contacts engages saidworkpiece adjacent the other end thereof;

first means for selectively forcing said first and second pairs ofcontacts between said first and second conditions;

third and fourth pairs of contacts spaced between said first and secondpairs of contacts respectively and from each other, each of said thirdand fourth pairs of contacts having a third opened condition and afourth workpiece clamping-and heatingco'ndition wherein when said thirdand fourth'contacts are in said fourth condition, said thirdpair of confirst means for supplying electrical current to saidfirst and thirdpairs of contactswhen' said first pair of contacts is in said secondcondition and said third pair of contacts is in said fourthcondition;and, 4 second means for supplying electrical current to said" second andfourth pairs of contacts when said-second pair of contacts is in saidsecond condition and said fourth pair of contacts is in said fourthcondition.

8. The apparatus as defined in claim 7 further including third means forsupplying electrical current to said first and second pairs of contactswhen said first and second pairs of contacts are in said secondcondition and said third and fourth pairs of contacts are in said thirdcondition.

9. The apparatus as defined in claim 8 wherein said first, second andthird supplying means comprise a single supplying means selectivelycontrollable for supplying electrical current to said first and third,said second and fourth and said first and second pairs of contacts.

10. In an apparatus for resistance heating an elongated workpiece havingfirst and second terminal end portions and an intermediate portionhaving an aperture with'two longitudinally spaced terminal areas, oneterminal area facing said first end portion and the other terminal areafacing said second end portion, said apparatus including first andsecond spaced contacts, first means for selectively forcing said firstand second contacts between a spaced apart condition and an electricalcontacting condition with said workpiece at said first and secondterminal end portions respectively and first means for causingelectrical current flow through said workpiece between said first andsecond contacts, the improvement comprising:

a third contact including second means for selectively forcing saidthird contact between a spaced apart condition and an electricalcontacting conditiOn with said workpiece at said one terminal area;

a fourth contact including third means forselectively forcing saidfourth contact between a spaced apart condition and an electricalcontacting condition with said workpiece at said other terminal area;

means for selectively causing an electrical current flow through saidworkpiece between said first and third contacts when said first andthird contacts are in said contacting conditions; and,

means for selectively causing an electrical current flow through saidworkpiece between said second and fourth contacts when said second andfourth contacts are in said contacting condition.

11. The improvement as defined in claim 10 wherein said third and fourthcontacts each comprise a pair of contacts, at least one contact in eachof said pairs being selectively movable relative to the other contact insaid pairs between said spaced apart conditions and ,said

electrical contacting conditions. r

1. A method of resistance heating an elongated workpiece having at leastone slot-like area extending generally longitudinally along a portion ofsaid workpiece, said method comprising the steps of: clamping saidworkpiece between first and second pairs of contacts at first and secondspaced positions along said workpiece; clamping said workpiece betweenthird and fourth pairs of contacts at third and fourth spaced positionsbetween said first and second positions respectively with said third andfourth positions each being disposed adjacent an end of said slot-likearea; and, causing an electrical current to flow through said workpiecebetween said first and third pairs of contacts and through saidworkpiece between said second and fourth pairs of contacts.
 2. Themethod as defined in claim 1 further including the steps of removingsaid third and fourth pairs of contacts from said clamping positionswhen the portions of said workpiece disposed between said first andthird pairs of contacts and said second and fourth pairs of contactshave been heated to a predetermined desired temperature; and, causing anelectrical current to flow through said workpiece between said first andsecond pairs of contacts to heat said elongated workpiece to apredetermined desired temperature.
 3. The method as defined in claim 1wherein said step of clamping said workpiece at first and second spacedpositions comprises the step of clamping said workpiece adjacent theends thereof.
 4. A method of heating an elongated workpiece having firstand second terminal end portions and an intermediate portion having anaperture therein, said method comprising the steps of: resistanceheating said terminal end portions; and, resistance heatingsubstantially the entire workpiece including said terminal end portionsand said intermediate portion.
 5. The method as defined in claim 4wherein the step of resistance heating said terminal end portionscomprises the steps of placing a first contact against said workpiece inelectrical contact with one of said terminal end portions; placing asecond contact against said workpiece in electrical contact with theother of said terminal end portions; placing a third contact againstsaid workpiece in electrical contact with said intermediate portion atthe end of said aperture adjacent said one of said terminal endportions; placing a fourth contact against said workpiece in electricalcontact with said intermediate portion at the end of said apertureadjacent said other of said terminal end portions; causing an electricalcurrent to flow through said workpiece between said first and said thirdcontacts; and, causing an electrical current to flow through saidworkpiece between said second and said fourth contacts.
 6. The method asdefined in claim 5 wherein the step of resistance heating substantiallythe entire workpiece comprises the steps or removing said third and saidfourth contacts from electrical contact against said intermediateportion and causing an electrical current to flow through said workpiecebetween said first and said second contacts.
 7. An apparatus fOrresistance heating an elongated workpiece having at least one slot-likearea extending longitudinally therealong, said apparatus comprising:first and second spaced apart pairs of contacts, each pair having afirst opened condition and a second workpiece clamping and heatingcondition wherein when said first and second pairs of contacts are insaid second condition, said first pair of contacts engages saidwOrkpiece adjacent one end thereof and said second pair of contactsengages said workpiece adjacent the other end thereof; first means forselectively forcing said first and second pairs of contacts between saidfirst and second conditions; third and fourth pairs of contacts spacedbetween said first and second pairs of contacts respectively and fromeach other, each of said third and fourth pairs of contacts having athird opened condition and a fourth workpiece clamping and heatingcondition wherein when said third and fourth contacts are in said fourthcondition, said third pair of contacts engages said workpiece adjacentone end of said slot-like area and said fourth pair of contacts engagessaid workpiece adjacent the other end of said slot-like area; means forselectively forcing said third and fourth pairs of contacts between saidthird and fourth conditions; first means for supplying electricalcurrent to said first and third pairs of contacts when said first pairof contacts is in said second condition and said third pair of contactsis in said fourth condition; and, second means for supplying electricalcurrent to said second and fourth pairs of contacts when said secondpair of contacts is in said second condition and said fourth pair ofcontacts is in said fourth condition.
 8. The apparatus as defined inclaim 7 further including third means for supplying electrical currentto said first and second pairs of contacts when said first and secondpairs of contacts are in said second condition and said third and fourthpairs of contacts are in said third condition.
 9. The apparatus asdefined in claim 8 wherein said first, second and third supplying meanscomprise a single supplying means selectively controllable for supplyingelectrical current to said first and third, said second and fourth andsaid first and second pairs of contacts.
 10. In an apparatus forresistance heating an elongated workpiece having first and secondterminal end portions and an intermediate portion having an aperturewith two longitudinally spaced terminal areas, one terminal area facingsaid first end portion and the other terminal area facing said secondend portion, said apparatus including first and second spaced contacts,first means for selectively forcing said first and second contactsbetween a spaced apart condition and an electrical contacting conditionwith said workpiece at said first and second terminal end portionsrespectively and first means for causing electrical current flow throughsaid workpiece between said first and second contacts, the improvementcomprising: a third contact including second means for selectivelyforcing said third contact between a spaced apart condition and anelectrical contacting conditiOn with said workpiece at said one terminalarea; a fourth contact including third means for selectively forcingsaid fourth contact between a spaced apart condition and an electricalcontacting condition with said workpiece at said other terminal area;means for selectively causing an electrical current flow through saidworkpiece between said first and third contacts when said first andthird contacts are in said contacting conditions; and, means forselectively causing an electrical current flow through said workpiecebetween said second and fourth contacts when said second and fourthcontacts are in said contacting condition.
 11. The improvement asdefined in claim 10 wherein said third and fourth contacts each comprisea pair of contacts, at least one contact in each of said pairs beingselecTively movable relative to the other contact in said pairs betweensaid spaced apart conditions and said electrical contacting conditions.